It's time to go after ISIS in Iraq and Syria, President Barack Obama said Wednesday night in a nationally televised address intended to sell stepped-up military efforts to a war-weary public.

Announcing a broad campaign against the Sunni jihadists who have rampaged from Syria across northern Iraq, Obama announced an escalated U.S. military role as part of a strategy that includes building an international coalition to support Iraqi ground forces and perhaps troops from other allies.

U.S. airstrikes have been hitting the jihadists in Iraq. Those strikes will be expanded to ISIS targets in Syria, Obama said.

"I have made it clear that we will hunt down terrorists who threaten our country, wherever they are," he said. "That means I will not hesitate to take action against ISIL in Syria, as well as Iraq. This is a core principle of my presidency: if you threaten America, you will find no safe haven."

The declaration answered calls from a growing number of U.S. politicians for such a step, with increasing public support.

"This was a very difficult speech for him to give," CNN chief political analyst Gloria Borger said of a president who campaigned on ending wars in Iraq and Afghanistan. "He's inserted us into the middle of a Syrian civil war."

More U.S. forces to Iraq

Obama also announced another 475 American military advisers would go to Iraq, pushing the total figure to about 1,700. At the same time, he made clear the strategy differed from all-out war again in Iraq less than three years after he withdrew combat forces from the country.

JUST WATCHED

Cruz: 'Photo-op' action won't stop ISIS

MUST WATCH

JUST WATCHED

Cheney: Obama must know we're at war

MUST WATCH

Cheney: Obama must know we're at war03:41

"It will not involve American combat troops fighting on foreign soil," Obama said.

His address from the White House also sought to convince allies and the nation of a firm U.S. commitment to lead an international coalition to fight the jihadists who rampaged across northern Iraq from Syria this year. They are known as ISIS, ISIL and Islamic State.

Noting the formation of a new Iraqi government, which his administration has demanded, Obama announced that "America will lead a broad coalition to roll back this terrorist threat."

Objective: "degrade and ultimately destroy" ISIS

"Our objective is clear: We will degrade, and ultimately destroy, ISIL through a comprehensive and sustained counterterrorism strategy," he said.

Senior administration officials who briefed reporters before the speech on condition of not being identified said airstrikes against ISIS targets in Syria would occur "at a time and place of our choosing."

"We're not going to telegraph our punches by being specific about the time and nature of the targets," one official said, adding that "we will do that as necessary as we develop targets."

Also Wednesday, Obama shifted $25 million in military aid to Iraqi forces, including Kurdish fighters in the north combating the ISIS extremists. The aid could include ammunition, small arms and vehicles, as well as military education and training, State Department spokeswoman Marie Harf said.

U.S. diplomatic efforts this week seek to solidify the coalition. Secretary of State John Kerry left Tuesday to push Sunni leaders in Jordan and Saudi Arabia to join the United States and its allies in combating ISIS, while Defense Secretary Chuck Hagel and Lisa Monaco, the homeland security adviser, also will be in the region.

Saudis part of coalition

"The Saudis made very clear that they support this mission, they will join us in this mission," a senior administration official said. "We are joined by very important Arab partners as well."

JUST WATCHED

The role of Sunnis in stopping ISIS

MUST WATCH

JUST WATCHED

Who's worse? ISIS or al Qaeda?

MUST WATCH

Who's worse? ISIS or al Qaeda?02:21

Obama has been criticized by conservatives and some Democrats for what they call a timid response so far to the threat by ISIS fighters. The recent beheading of two American journalists held captive by ISIS raised public awareness of the extremists and the threat they pose.

"We can't erase every trace of evil from the world, and small groups of killers have the capacity to do great harm. That was the case before 9/11, and that remains true today," Obama said.

ISIS poses a threat to the Middle East, including the people of Iraq and Syria, he said, adding: "If left unchecked, these terrorists could pose a growing threat beyond that region, including the United States."

"The next phase is offense"

Conservative Republicans who have railed against Obama's foreign policy sounded relieved by what they heard.

"The President's plan announced this evening is an encouraging step in the right direction," said GOP Rep. Mike Rogers, who chairs the House Intelligence Committee and has been a harsh Obama critic. "Success will depend on the details of its implementation."

His Republican colleage, Rep. Michael McCaul of Texas, said: "Tonight the President seemed to have faced reality."

Leading Democrats such as Sen. Dianne Feinstein of California and Sen. Chuck Schumer of New York praised the speech, as expected, while Sen. Robert Menendez of New Jersey said the Foreign Relations Committee he chairs would begin drafting legislation to provide Obama with specific authority under the War Powers Resolution to continue to extend military operations against ISIS.

Meanwhile, the anti-war liberal caucus in the House signaled possible opposition by calling for a vote on authorizing expanded military action.

Congressional authority

Obama has insisted he has the authority to ratchet up airstrikes against ISIS under war powers granted more than a decade ago to fight al Qaeda. ISIS formed from some al Qaeda affiliates but is separate from the central leadership of the terrorist organization behind the September 11, 2001, attacks on the United States.

This week, he asked Congress for additional authority to arm and train moderate Syrian rebels to fight the ISIS extremists, effectively shifting a covert operation by the CIA to a mission led by the Defense Department.

Such authority comes under Title 10 of the U.S. code, which deals with military powers, and Congress could vote on granting it next week. Approval also would allow the United States to accept money from other countries for backing the Syrian opposition forces.

Most voices in Congress back strong U.S. action against the ISIS fighters. However, any vote on military action can be risky, especially with congressional elections less than two months off.

Fraught politics

The fraught politics of the issue were clear when House Republican leaders put off a vote on a government spending measure set for Wednesday after pressure emerged to add the Title 10 authorization to it.

Obama initially rejected arming the Syrian opposition against President Bashar al-Assad more than two years ago to avoid getting mired in another Middle East conflict. U.S. officials also feared American weapons could end up in the hands of extremists, such as al Qaeda affiliates that eventually morphed into ISIS.

As the tide has turned against Syria's opposition, which now finds itself fighting both government forces and ISIS, the United States began its covert aid to some rebel factions.

"Now we have a two-year track record of relationships with the Syrian opposition," a senior administration official said. "We have far greater confidence in who we are dealing with."

Until now, the U.S. strategy against ISIS has included airstrikes on the extremists in Iraq to protect several hundred American military personnel there while helping the Iraqis and providing humanitarian support.

Veteran diplomat: ISIS worse than al Qaeda

Calls for a more forceful campaign against ISIS have increased in recent months.

Former U.S. ambassador Ryan Crocker, who served in Syria, Iraq, Afghanistan and Pakistan, told CNN on Wednesday that ISIS presents a bigger threat to America than al Qaeda.

"They are more numerous, they are better armed, they are far better financed, they are better experienced, and perhaps most critically there are several thousand of them who hold Western passports, including American passports," Crocker said. "They don't need to get a visa; they just need to get on a plane."

He added: "If we don't think we're on their target list, we are delusional."